Salem Steel Plant (SSP), a unit of Steel Authority of India Limited (SAIL), is a steel plant involved in the production of stainless steel. It is located along the Salem — Bangalore National Highway 44 in the foothills of Kanjamalai in Salem district, Tamil Nadu, India. The plant has an installed capacity of 70,000 tonnes per annum in its cold rolling mill and 3,64,000 tonnes per annum in the hot rolling mill. It also has the country's first stainless steel blanking facility.
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The present study describes the enhancement of microstructural and mechanical properties by pulse mode of metal transfer in welded modified ferritic stainless steel (409 M) sheets (as received) of 4 mm thickness. The welded joints were prepared by varying modes of metal transfer at different heat input conditions (i.e. pulse mode at 0.5 kJ/mm and 0.9 kJ/mm and spray mode at 0.5 kJ/mm), using austenitic filler wire (i.e. 308 L) under Ar + 10% CO2 atmosphere. It has been observed that the pulse mode of metal transfer significantly alters the weld metal composition compare to spray mode which promotes comparatively stable austenite in the welds and also depicts significant enhancement in grain structure even with the higher heat input condition. Present study clearly shows that pulse mode enhances micro-hardness of welded joints and toughness values of weld metals compare to spray mode of metal transfer for a particular heat input.
The present study describes in detail the effect of shielding gas mixtures on the bead geometry, microstructure, and mechanical properties of gas metal arc welded modified ferritic stainless steel (409M) sheets (as received) of 4 mm thickness. The welded joints were prepared under spray (S) mode of metal transfer at same heat input using 308L austenitic filler metal and four different shielding gas mixtures, i.e., pure Ar, Ar + 5% CO2, Ar + 10% CO2, and Ar + 20% CO2. The welded joints were evaluated by means of microstructural changes, hardness, tensile strength, and toughness. The dependence of weld metal microstructure on shielding gas mixtures has been determined by bead geometry, Cr-eq/Ni-eq ratio, M-s, M-epsilon s, optical microscopy (OM), transmission electron microscopy (TEM), and electron probe microanalyzer (EPMA). It was observed that the variation in shielding gas mixture effectively manipulates the solid-state phase transformation and precipitation behavior of the welded joints. Variations in microstructure ultimately affect the mechanical properties of the weld metal as well as coarse-grained HAZ (CGHAZ). The present study concluded that up to 10% CO2 may be commercially utilized in the shielding gas mixture for fabricating waded joints of 409M using 308L filler metal without deteriorating microstructural and mechanical properties.
Metastable austenitic stainless steel type 301LN is widely used for fabrication of structural components of Metro Coaches. The steel exhibits both high strength and enhanced plasticity due to strain hardening as well as formation of strain-induced martensite (alpha') during cold deformation (TRIP effect). The current market requirement, as projected by many of the ongoing Metro Rail Projects in India, calls for manufacture of this steel with ultimate tensile strength (UTS) in excess of 1000 MPa and yield (YS/UTS) ratio of less than 0.8, as this would facilitate substantial reductions in tare weight and crash-worthiness of metro coaches. The typical property requirements in high temper (HT) as per one typical Metro Coach specification are: Yield Strength (YS) similar to 751-921 MPa, Ultimate Tensile Strength (UTS) similar to 1001-1151 MPa, Elongation similar to 22% min, Hardness 36 HRC max and YS/UTS ratio <0.8. Previous plant experience has shown that the maximum attainable UTS in this grade through cold rolling is only to the tune of 970 MPa and any excess deformation severely impairs both ductility (< 22%) and hardness (>36 HRC) beyond acceptable limits. In the present work, an innovative thermomechanical processing (TMP) methodology has been evolved for the attainment of this seemingly unlikely combination of properties through experimental cold rolling and short annealing simulations in Gleeble 3500 C thermomechanical simulator. The novel process methodology entails imparting heavy cold reductions (CR) of 45-50% in Sendzimir Mill followed by brief/ short reversion annealing treatments (80-160 s) by means of single furnace operation at 750 degrees C at standard line operating speeds for 300 series in Annealing Pickling Line-1 (AP Line-1) of Salem Steel Plant (SSP) in India. The improvement in properties (strength-ductility combination) has been attributed to grain refinement through formation of submicron grained austenitic (gamma) microstructure by controlled reversion of strain-induced martensite (alpha') during the short annealing treatment. The process is distinct from conventional long annealing treatments (300-360 s), which are employed to soften the steel after cold rolling by means of recovery and recrystallization processes.
Metastable austenitic stainless steel type 301LN is widely used for fabrication of structural components of Metro Coaches. The steel exhibits both high strength and enhanced plasticity due to strain hardening as well as formation of strain-induced martensite (α) during cold deformation (TRIP effect). The current market requirement, as projected by many of the ongoing Metro Rail Projects in India, calls for manufacture of this steel with ultimate tensile strength (UTS) in excess of 1000 MPa and yield (YS/UTS) ratio of less than 0.8, as this would facilitate substantial reductions in tare weight and crash-worthiness of metro coaches. The typical property requirements in high temper (HT) as per one typical Metro Coach specification are: Yield Strength (YS) ~ 751-921 MPa, Ultimate Tensile Strength (UTS) ~ 1001-1151 MPa, Elongation ~ 22% min, Hardness ~ 36 HRC max and YS/UTS ratio <0.8. previous="" plant="" experience="" has="" shown="" that="" the="" maximum="" attainable="" uts="" in="" this="" grade="" through="" cold="" rolling="" is="" only="" to="" tune="" of="" 970="" mpa="" and="" any="" excess="" deformation="" severely="" impairs="" both="" ductility="" 22="" hardness=""> 36 HRC) beyond acceptable limits. In the present work, an innovative thermomechanical processing (TMP) methodology has been evolved for the attainment of this seemingly unlikely combination of properties through experimental cold rolling and short annealing simulations in Gleeble 3500 C thermomechanical simulator. The novel process methodology entails imparting heavy cold reductions (CR) of 45-50% in Sendzimir Mill followed by brief/ short reversion annealing treatments (80-160 s) by means of single furnace operation at 750 °C at standard line operating speeds for 300 series in Annealing Pickling Line-1 (AP Line-1) of Salem Steel Plant (SSP) in India. The improvement in properties (strength-ductility combination) has been attributed to grain refinement through formation of submicron grained austenitic (γ) microstructure by controlled reversion of strain-induced martensite (α) during the short annealing treatment. The process is distinct from conventional long annealing treatments (300-360 s), which are employed to soften the steel after cold rolling by means of recovery and recrystallization processes.
